Dengue virus

I. Organism Information

A. Taxonomy Information
  1. Species:
    1. Dengue virus type 1 :
      1. Ontology: UMLS:C0011313
      2. GenBank Taxonomy No.: 11053
      3. Description: Dengue fever and dengue hemorrhagic fever (DF/DHF) are caused by the dengue viruses, which belong to the genus Flavivirus, family Flaviviridae. There are four antigenically related, but distinct, dengue virus serotypes (DEN-1, DEN-2, DEN-3 and DEN-4), all of which can cause DF/DHF (Gubler, 1997). All analyses undertaken to date show that the four serotypes of dengue virus are phylogenetically distinct, and often to the same degree as different "species" of flaviviruses (Holmes and Twiddy, 2003). The first dengue viruses were isolated from soldiers who became ill in Calcutta, India, New Guinea, and Hawaii. The viruses from India, Hawaii, and one strain from New Guinea were antigenically similar, whereas three other strains from New Guinea appeared to be different. They were called dengue 1 (DEN-1) and dengue 2 (DEN-2) and designated as prototype viruses (DEN-1, Hawaii and DEN-2, New Guinea-C) (Gubler, 1988).
      4. Variant(s):
        • Dengue virus type 1 (strain 924-1) :
          • GenBank Taxonomy No.: 11056
          • Parent: Dengue virus type 1
          • Description: Four DEN-1 virus strains were isolated from humans with classical DF: AHF82-80 (Thailand 1980), 836-1 (Philippines 1984, strain 162, AP2), 924-1 (Mexico 1983, strain 1378) and CV1636/77 (Jamaica 1977) (Chu et al., 1989).
        • Dengue virus type 1 (strain TH-SMAN) :
          • GenBank Taxonomy No.: 31633
          • Parent: Dengue virus type 1
          • Description: TH-36 was isolated in 1958 by Hammon and co-workers from a patient with DHF in Bangkok. TH-Sman was isolated from a similar patient by Dr. Sman Vardhanabhuti (Shiu et al., 1992).
        • Dengue virus type 1 (strain Western Pacific) :
          • GenBank Taxonomy No.: 11059
          • Parent: Dengue virus type 1
          • Description: Western Pacific strain (West Pac) of DEN-1, isolated from a patient with a mild case of DF in 1974 (Puri et al., 1998). The parent DEN-1 strain used in these studies, 45AZ5 PDK-0, was derived from the human isolate, West Pac 74, made from a mild case of dengue fever during an outbreak on Nauru Island in the Western Pacific in 1974 (Puri et al., 1997).
    2. Dengue virus type 2 :
      1. Ontology: UMLS: C0318759
      2. GenBank Taxonomy No.: 11060
      3. Description: The first dengue viruses were isolated from soldiers who became ill in Calcutta, India, New Guinea, and Hawaii. The viruses from India, Hawaii, and one strain from New Guinea were antigenically similar, whereas three other strains from New Guinea appeared to be different. They were called dengue 1 (DEN-1) and dengue 2 (DEN-2) and designated as prototype viruses (DEN-1, Hawaii and DEN-2, New Guinea-C) (Gubler, 1988).
      4. Variant(s):
        • Dengue virus type 2 (isolate Malaysia M1) :
          • GenBank Taxonomy No.: 11061
          • Parent: Dengue virus type 2
          • Description: Dengue-2 (DEN-2) viruses, MI, M2 and M3, isolated in Malaysia from patients with dengue haemorrhagic fever, dengue shock syndrome and dengue fever, respectively (Fong et al., 1990).
        • Dengue virus type 2 (isolate Malaysia M2) :
          • GenBank Taxonomy No.: 11062
          • Parent: Dengue virus type 2
          • Description: Dengue-2 (DEN-2) viruses, MI, M2 and M3, isolated in Malaysia from patients with dengue haemorrhagic fever, dengue shock syndrome and dengue fever, respectively (Fong et al., 1990).
        • Dengue virus type 2 (isolate Malaysia M3) :
          • GenBank Taxonomy No.: 11063
          • Parent: Dengue virus type 2
          • Description: Dengue-2 (DEN-2) viruses, MI, M2 and M3, isolated in Malaysia from patients with dengue haemorrhagic fever, dengue shock syndrome and dengue fever, respectively (Fong et al., 1990).
        • Dengue virus type 2 (strain 16681-PDK53) :
        • Dengue virus type 2 (strain TH-36) :
          • GenBank Taxonomy No.: 31637
          • Parent: Dengue virus type 2
          • Description: TH-36 was isolated in 1958 by Hammon and co-workers from a patient with DHF in Bangkok (Shiu et al., 1992). In 1958 an epidemic of hemorrhagic fever occurred in and near Bangkok, Thailand during the rainy season. The disease there was called Thai hemorrhagic fever. Over 2500 patients were hospitalized with about 10% case fatality rate. During the epidemic, Hammon et al. isolated several viruses both from human sera and from Aedes aegypti. Among these isolates a prototype strain named TH-36 (representing a number of apparently identical isolates) was found to be antigenically closely related to dengue type 2 (Ibrahim et al.,1968).
    3. Dengue virus type 3 :
      1. Ontology: UMLS:C0318760
      2. GenBank Taxonomy No.: 11069
      3. Description: The first dengue viruses were isolated from soldiers who became ill in Calcutta, India, New Guinea, and Hawaii. The viruses from India, Hawaii, and one strain from New Guinea were antigenically similar, whereas three other strains from New Guinea appeared to be different. They were called dengue 1 (DEN-1) and dengue 2 (DEN-2) and designated as prototype viruses (DEN-1, Hawaii and DEN-2, New Guinea-C). Two more serotypes-dengue 3 (DEN-3) and dengue 4 (DEN-4)-were subsequently isolated from patients with a hemorrhagic disease during an epidemic in Manila in 1956 (Gubler, 1988).
    4. Dengue virus type 4 :
      1. Ontology: UMLS:C0318761
      2. GenBank Taxonomy No.: 11070
      3. Description: The first dengue viruses were isolated from soldiers who became ill in Calcutta, India, New Guinea, and Hawaii. The viruses from India, Hawaii, and one strain from New Guinea were antigenically similar, whereas three other strains from New Guinea appeared to be different. They were called dengue 1 (DEN-1) and dengue 2 (DEN-2) and designated as prototype viruses (DEN-1, Hawaii and DEN-2, New Guinea-C). Two more serotypes-dengue 3 (DEN-3) and dengue 4 (DEN-4)-were subsequently isolated from patients with a hemorrhagic disease during an epidemic in Manila in 1956 (Gubler, 1988).
B. Lifecycle Information :
  1. Virion :
    1. Size: 40 to 60 nm in diameter, containing an electron dense core (about 30 nm in diameter) surrounded by a lipid bilayer (Lindenbach and Rice, 2001).
    2. Shape: Dengue viruses are spherical, lipid-enveloped viruses (Guzman and Kouri, 2004).
    3. Picture(s):
      1. Dengue 2 virus particles (Pacific Center for Emerging Infectious Diseases Research):



        Description: Mature particles of Dengue-2 replicating in tissue culture (Pacific Center for Emerging Infectious Diseases Research).
    4. Description: Flavivirus virions consist of a spherical ribonucleoprotein core surrounded by a lipoprotein envelope with small surface projections. The projections seen in electron micrographs are clarified by x-ray crystallography and represent molecules of envelope glycoprotein, which form rodlike structures anchored to the viral membrane at their basal ends. Envelope lipids constitute about 17% of the virion dry weight and are derived from the host cell lipids (Burke and Monath, 2001).

  2. Description: Dengue virus is transmitted in a cycle involving humans and mosquitoes, Aedes aegypti being the most important vector (Burke and Monath, 2001). Two distinct transmission cycles have been described for DENV: Endemic and epidemic cycles that occur in urban/periurban environments and involve human reservoir and amplification hosts. The peridomestic mosquito Ae. aegypti is the principal DENV vector, with Ae. albopictus and other anthropophilic Aedes mosquitoes serving as secondary vectors. Ecologically distinct, sylvatic, enzootic cycles of DENV occur in west Africa and Malaysia, probably involving non-human primate reservoir hosts and sylvatic Aedes spp. mosquito vectors. The two kinds of DENV cycles are also evolutionarily distinct, and all four serotypes of endemic/epidemic DENV are believed to have evolved independently from sylvatic progenitors during the past few 1,000 years (Diallo et al., 2005).
  3. Transmission of Dengue Virus by Aedes aegypti (CDC Dengue Slideset):



    Description: The transmission cycle of dengue virus by the mosquito Aedes aegypti begins with a dengue-infected person. This person will have virus circulating in the blood-a viremia that lasts for about five days. During the viremic period, an uninfected female Aedes aegypti mosquito bites the person and ingests blood that contains dengue virus. Although there is some evidence of transovarial transmission of dengue virus in Aedes aegypti, usually mosquitoes are only infected by biting a viremic person. Then, within the mosquito, the virus replicates during an extrinsic incubation period of eight to twelve days. The mosquito then bites a susceptible person and transmits the virus to him or her, as well as to every other susceptible person the mosquito bites for the rest of its lifetime. The virus then replicates in the second person and produces symptoms. The symptoms begin to appear an average of four to seven days after the mosquito bite-this is the intrinsic incubation period, within humans. While the intrinsic incubation period averages from four to seven days, it can range from three to 14 days. The viremia begins slightly before the onset of symptoms. Symptoms caused by dengue infection may last three to 10 days, with an average of five days, after the onset of symptoms-so the illness persists several days after the viremia has ended (Source: CDC) (CDC Dengue Slideset).
C. Genome Summary:
  1. Genome of Dengue virus type 1 (strain Western Pacific)
    1. Description: The four serotypes of dengue (DEN) virus belong to the genus Flavivirus in the family Flaviviridae. These are single-stranded positive-sense RNA viruses with a genome of about 11000 bases that codes for three structural proteins, C-prM-E; seven nonstructural proteins, NS1-NS2a-NS2b-NS3-NS4a-NS4b-NS5; and short non-coding regions on both the 5' and 3' ends (Puri et al., 1997).
    2. Chromosome:
      1. GenBank Accession Number: NC_001477
      2. Size: 10735 bp ss-RNA (NCBI Entrez Genome).
      3. Gene Count: The genome of flaviviurses consists of a single-stranded RNA about 11 kilobases (kb) in length. This RNA contains a 5' cap [m(7)G51ppp5'A) at the 51 end and lacks a polyadenylate tail. Genomic RNA is the messenger RNA for translation of a single long open reading frame (ORF) as a large polyprotein (Lindenbach and Rice, 2001).
      4. Description: The complete nucleotide sequences of the genomes of dengue-1 virus virulent 45AZ5 PDK-O and attenuated vaccine candidate strain 45AZ5 PDK-27 have been determined and compared with the dengue-1 virus Western Pacific (West Pac) 74 parent strain from which 45AZ5 PDK-O was derived. Twenty-five (0.23%) nucleotide and 10 (0.29%) amino acid substitutions occurred between parent strain dengue-1 virus West Pac 74 and virulent strain 45AZ5 PDK-O, which was derived from the parent by serial passage in diploid foetal rhesus lung (FRhL-2) and mutagenized with 5-azacytidine. These substitutions were preserved in the 45AZ5 PDK-27 vaccine. 45AZ5 PDK-O and PDK-27 strains, which differ by 27 passages in primary dog kidney (PDK) cells, show 25 (0.23%) nucleotide and 11 (0.32%) amino acid divergences. These comparative studies suggest that the changes which occurred between the West Pac 74 and 45AZ5 PDK-O strains may alter the biological properties of the virus but may not be important for attenuation. Important nucleotide base changes responsible for attenuation accumulated between 45AZ5 PDK-O and 27 (Puri et al., 1997).

  2. Genome of Dengue virus type 2 (strain PR159/S1)
    1. Chromosome:
      1. GenBank Accession Number: NC_001474
      2. Size: 10703 bp ss-RNA (NCBI Entrez Genome)
      3. Description: We have determined the complete sequence of the RNA of dengue 2 virus (S1 candidate vaccine strain derived from the PR-159 isolate) with the exception of about 15 nucleotides at the 5' end. The genome organization is the same as that deduced earlier for other flaviviruses and the amino acid sequences of the encoded dengue 2 proteins show striking homology to those of other flaviviruses. The overall amino acid sequence similarity between dengue 2 and yellow fever virus is 44.7%, whereas that between dengue 2 and West Nile virus is 50.7%. These viruses represent three different serological subgroups of mosquito-borne flaviviruses. Comparison of the amino acid sequences shows that amino acid sequence homology is not uniformly distributed among the proteins; highest homology is found in some domains of nonstructural protein NS5 and lowest homology in the hydrophobic polypeptides ns2a and 2b. In general the structural proteins are less well conserved than the nonstructural proteins. Hydrophobicity profiles, however, are remarkably similar throughout the translated region. Comparison of the dengue 2 PR-159 sequence to partial sequence data from dengue 4 and another strain of dengue 2 virus reveals amino acid sequence homologies of about 64 and 96%, respectively, in the structural protein region. Thus as a general rule for flaviviruses examined to date, members of different serological subgroups demonstrate 50% or less amino acid sequence homology, members of the same subgroup average 65-75% homology, and strains of the same virus demonstrate greater than 95% amino acid sequence similarity (Hahn et al., 1988).

  3. Genome of Dengue virus type 3
    1. Chromosome:
      1. GenBank Accession Number: NC_001475
      2. Size: 10,696 bp ss-RNA (NCBI Entrez Genome).
      3. Description: The complete nucleotide sequence of the genome of the dengue virus type 3 was determined. Sequence analyses of the genomic RNA and cloned cDNA revealed that the genomic RNA contains 10,696 nucleotides and encodes a single open reading frame of 10,170 nucleotides corresponding to 3390 amino acid residues. The N-terminal amino acid sequences of three structural proteins (C, M, and E proteins) and the preM protein were also determined from the purified virion. When the deduced amino acid sequence and N-terminal amino acid sequence determined from purified proteins were compared with those of other flaviviruses, the genome organization was found to be the same as that of other flaviviruses (Osatomi and Sumiyoshi, 1990).

  4. Genome of Dengue virus type 4
    1. Chromosome:
      1. GenBank Accession Number: NC_002640
      2. Size: 10,649 bp ss-RNA (NCBI Entrez Genome).
      3. Description: Unpublished sequence (NCBI Entrez Genome).

II. Epidemiology Information

The first reported epidemics of dengue-like disease occurred on three separate continents almost simultaneously in 1779 and 1780. Although there is some disagreement as to whether all of these epidemics were caused by dengue viruses, it is clear that dengue and other arboviruses with similar ecology had widespread distribution in the tropics as long as 200 years ago. For the next 175 years major pandemics of dengue-like illness, occurred in Asia and the Americas at variable intervals ranging from 10 to 30 years. With the advent of modern diagnostic virology, and the isolation and identification of the four dengue virus serotypes, their distribution became better known. Asia historically has been the area of highest endemicity, with all four dengue serotypes circulation in the large urban centers of most countries. During and shortly after World War II, Ae. aegypti became more widespread in Asia, and with the subsequent urbanization that occurred in most countries, the incidence of dengue infection increased dramatically. This increase coincided with the emergence of epidemic DHF in the 1950s (Gubler, 1988). The factors responsible for this global resurgence of DF and the emergence of DHF include unprecedented population growth, unplanned and uncontrolled urbanisation, increased air travel, the lack of effective mosquito control, and the deterioration, during the past 30 years, of public health infrastructure (Rigau-Perez et al., 1998). The average number of DF/DHF cases reported to WHO per year has risen from 908 between 1950 and 1959 to 514,139 between 1990 and 1999. The real figure is estimated to be closer to 50 million cases a year causing 24,000 deaths. Of an estimated 500,000 cases of DHF/DSS requiring hospitalisation each year, roughly 5% die according to WHO statistics (Guha-Sapir and Schimmer, 2005).

A. Outbreak Locations:
  1. Asia. Epidemic DF was a common occurrence in Asia in the first 50 years of the 20th century. Epidemic waves would move through the region every 10 to 40 years, depending on when a new virus was introduced. DEN viruses were endemic in many cities of Asia during this time as documented by the numerous accounts of expatriates arriving in a tropical Asian city only to become ill with a severe dengue-like illness within weeks to months of arrival (Gubler, 2004).
  2. Maldives. Maldives has experienced an outbreak of dengue since January 2006, with 602 suspected cases until 5 March 2006 (including 64 cases of dengue haemorrhagic fever and 9 cases of dengue shock syndrome) (Weekly Epidemiological Record, 2006).
  3. India. The new dengue paradigm viz, the burst of sudden disease activity, persistence and diffusion of the disease in different areas has secured a foot-hold in Southern India and has emerged as a serious public health problem. In Tamil Nadu, annual reports of dengue cases and deaths due to dengue were ranging from 128 to 264 and 2 to 21 respectively up to the year 2000. Recently, between October 2001 and January 2002, an epidemic of dengue emerged in Chennai, Tamil Nadu, affecting adults and children; majority of the victims were children less than 15 yrs of age (Kabilan et al., 2005). Between October 2001 and January 2002, there was an epidemic of dengue in Chennai, with a peak in October. The case occurrence was reported to be high among pediatric group. The number of cases confirmed during the study period was considered as the representative of the cases reported (about 700 cases) to the health surveillance system in Chennai (Kabilan et al., 2005). In India, dengue virus activity has been reported in many parts of the country with sudden epidemics over the last few years. Seasonal and cyclic epidemic pattern of dengue is a recent phenomenon in Northern India. The DF, DHF and DSS have spread dramatically in many parts of the country. Though all age groups were affected in these epidemics, the occurrence was high among children more than 6 yr; and few infants also presented symptoms of DHF (Kabilan et al., 2005).
  4. Timor-Leste. As of 28 February 2005, WHO has received reports of 336 hospitalized cases of dengue infection and 22 deaths.Of the 336 cases, 263 had clinical features compatible with dengue haemorrhagic fever (DHF) and the remaining 73 cases were diagnosed as having suspected dengue fever (DF)using WHO standard case definitions. Districts reporting DF/DHF cases are Baucau, Dili, Ermera, Liquica, Maliana, Manatuto and Viqueque, with 76% of the cases reported from Dili. Preliminary laboratory results have identified Dengue 3 as the main circulating strain in this outbreak (Weekly Epidemiological Record, 2005).
  5. Cuba. During the past three decades there have been four major dengue epidemics in Cuba. The first which was widespread throughout Cuba occurred in 1977 and only dengue fever was observed. This epidemic was caused by an American genotype DENV-1 virus. Subsequently, two independent DHF epidemics caused by DENV-2 of Asiatic origin occurred in 1981 throughout Cuba and 1997 in Santiago de Cuba, four and twenty years respectively, after the epidemic caused by DENV-1 (Rodriguez-Roche et al., 2005)
  6. Brazil. The following study was intended to evaluate the occurrence of typical signs and symptoms in the cases of classic dengue and hemorrhagic dengue fever, during the 2001-2002 epidemic in the city of Rio de Janeiro. The authors reviewed 155,242 cases notified to the Information System of Notification Diseases, from January/2001 to June/2002: 81,327 cases were classified as classic dengue and 958 as hemorrhagic dengue fever, with a total of 60 deaths (Casali et al., 2004).
  7. In early 2004, an outbreak of dengue began to spread throughout Indonesia. On 16 February 2004, the Indonesian Ministry of Health declared a national DF/DHF epidemic. Jakarta, the capital city with approximately 16 million inhabitants, was the most affected area (Suwandono et al., 2006) The Indonesian Ministry of Health reported cases of DF in 30 of 32 providences within the archipelago. In the capital city of Jakarta, a total of 20 503 cases were recorded, with an epidemic peak between March and April (Suwandono et al., 2006).
  8. Palau. An epidemic of dengue 4 virus occurred in the island nation of Palau between January and July 1995. The last known epidemic of dengue in the Palau Islands occurred in 1988 when dengue type 2 was introduced. Before that, dengue transmission had not been reported since 1944. In 1995, higher than expected rainfall for January and February may have contributed to a large mosquito population and increased transmission of the virus. Increased rainfall has been reported previously to be associated with epidemic dengue fever (Ashford et al., 2003). During January and February 1995, 145 patients (an unusually high number) with viral syndrome were reported to the Palau Ministry of Health. On April 3, 1995, a 38-year-old man died at the Palau National Hospital soon after presentation with viral syndrome. He was noted to have had neutropenia and thrombocytopenia. Initially, an outbreak of leptospirosis was suspected (and later this patient was confirmed to have leptospirosis by immunohistochemical analysis). However, the majority of the initial serum samples from patients with febrile illness tested at the Centers for Disease Control and Prevention (CDC) Dengue Laboratory in San Juan, Puerto Rico were consistent with dengue virus infection, suggesting an outbreak of dengue fever (Ashford et al., 2003).
B. Transmission Information:
  1. Ontology: UMLS:C0417744 From: Mosquito To: Human
    Mechanism: After the mosquito becomes infective, it may transmit dengue by taking a blood meal, or by simply probing the skin of a susceptible person (Rigau-Perez et al., 1998)

  2. From: Human To: Mosquito
    Mechanism: The mosquito becomes infected by a blood meal from a viraemic person and becomes infective after an obligatory extrinsic incubation period of 10-12 days (Rigau-Perez et al., 1998).

  3. Ontology: UMLS:C1444005 From: Human To: Human
    Mechanism: Vertical transmission of dengue virus has been recorded in a small number of cases, leading to neonatal DF or even DSS. One case of nosocomial transmission from a needlestick injury has been reported (Rigau-Perez et al., 1998). The vertical transmission of dengue has been infrequently described world-wide, although there are reports from Cuba, Brazil, Malaysia, and Thailand which have occurred during outbreaks. These report variable neonatal outcomes, from asymptomatic infection to death (Perret et al., 2005).

  4. From: Mosquito To: Mosquito
    Mechanism: It was originally thought that all vertical transmission of arboviruses in mosquitoes was transovarial in nature because viral antigen has been demonstrated in developing eggs for bunyaviruses, and both bunyaviruses and flaviviruses have been recovered from progeny reared from surface-sterilized eggs. It was eventually discovered, however, that vertical transmission of dengue viruses, and at least certain other flaviviruses, takes place in the genital chamber of the female as mature eggs are fertilized during oviposition. This explains how vertical transmission of dengue viruses can occur without virus in developing eggs (Rodhain and Rosen, 1997). Progeny of Aedes aegypti mosquitoes infected intrathoracically with dengue-3 virus was reared to subsequent generations. In each generation, blood-fed females were confined individually and the eggs obtained from the transovarially infected females were pooled. The seventh generation obtained from the infected parental mosquitoes showed that virus could persist in mosquitoes in successive generations through transovarial passage. The rate of vertical transmission initially increased in the few generations (F1-F2), but in subsequent generations it was found to be steady (Joshi et al., 2002). These observations, which have great epidemiologic importance, suggest that vector mosquitoes may play an important role in the maintenance of virus in nature, and that mosquitoes may act as reservoirs of these viruses (Joshi et al., 2002). Male Ae. albopictus can transmit dengue virus sexually in the course of mating, and females can transmit it vertically more efficiently than can Ae. aegypti females. These two mechanisms could explain the maintenance of the virus in nature between epidemics in non-endemic areas where susceptible human or primate populations are not always present (Gratz, 2004).

C. Environmental Reservoir:
  1. Humans :
    1. Ontology: UMLS:C0020114
    2. Description: Human dengue viruses are mostly active in urban areas where the virus is maintained through a cycle in which humans are the principal reservoir host and Aedes aegypti is the principal mosquito vector (de Silva et al., 1999).
    3. Survival Information: Dengue infection can cause a spectrum of illness ranging from mild, undifferentiated fever to illness up to 7 days' duration with high fever, severe headache, retro-orbital pain, arthralgia and rash, but rarely causing death (Guha-Sapir and Schimmer, 2005).
  2. Aedes mosquitoes :
    1. Ontology: UMLS:C0322859
    2. Description: The evidence that some Aedes (Stegomyia) species transmit dengue virus vertically suggests that they also could serve as reservoirs of the virus during dry season. their role in the epidemiology of dengue is not known in detail (Rodhain and Rosen, 1997).
    3. Survival Information: Dengue viruses multiply in the midgut epithelium, brain, fat body, and salivary glands of mosquitoes. No detectable pathologic changes result from infection, and mosquitoes remain infectious for life (Burke and Monath, 2001).
  3. Nonhuman Primates :
    1. Ontology: UMLS:C0237798
    2. Description: One or more dengue serotypes, transmitted by Aedes of the niveus group circulate in the forest canopy in primeval cycle among certain species of monkeys (Macaca sp. and Presbytis sp.-which have asymptomatic infections) in a silent cycle. Man is only occasionally involved in this cycle. Such a zoonotic reservoir of infection could exist in all the primary forests of tropical Asia: in Malaysia, in thailand, in Vietnam, in Cambodia, in Indonesia etc (Rodhain, 1991).
    3. Survival Information: There is considerable field evidence from both Malaysia and Africa that lower primates are involved in forest maintenance cycles of dengue viruses. Moreover, experimental laboratory data show that chimpanzees, gibbons, and macaque are susceptible to infection with dengue viruses. All species develop detectable viremia in the absence of clinical illness. The experimental infection data suggest that dengue viruses have become well adapted to lower primates which, therefore, are not useful as laboratory animal models for the study of human disease (Gubler, 1988).
D. Intentional Release:

No release information is currently available here.

III. Infected Hosts

  1. Human:
    1. Taxonomy Information:
      1. Species:
        1. Human :
          • Ontology: UMLS:C0086418
          • GenBank Taxonomy No.: 9606
          • Scientific Name: Homo sapiens (NCBI Taxonomy)
          • Description: Humans are the major host of dengue virus (Holmes and Twiddy, 2003). There is no consensus on when dengue first appeared in human populations, largely because its symptoms are often not diagnostic. The earliest record suggested is from a Chinese medical encyclopaedia dating to 992 A.D.. However, it is generally agreed that by the late 18th century a disease bearing a strong resemblance to dengue was causing intermittent epidemics in Asia and the Americas, and that by the late 19th and early 20th centuries the virus was probably widespread in the tropics and subtropics. Shortly after World War II, a new dengue-associated disease was reported in endemically infected areas of Southeast Asia. This had a far more pronounced impact than DF, since the primary targets were children. The first well documented outbreak of what came to be known as dengue haemorrhagic fever took place in Manila in 1953/54, and was followed by a larger outbreak in Bangkok in 1958. Since this time DHF/DSS have become endemic in all countries in Southeast Asia, with dramatic increases in case numbers, so much so that dengue is considered an archetypal "emerging" disease (Holmes and Twiddy, 2003).

    2. Infection Process:
      1. Description: Dengue viruses are efficiently transmitted in an urban cycle which involves man and Aedes aegypti, a day-biting species which often breeds in the clean water stored in houses. Infection with one type results in life-long immunity to that type but, after a short period of cross protection, individuals may become clinically ill during and infection with a second type (Halstead, 1988).
        • Aedes aegypti Mosquito (CDC Dengue Slideset):



          Description: The most common epidemic vector of dengue in the world is the Aedes aegypti mosquito. It can be identified by the white bands or scale patterns on its legs and thorax (CDC Dengue Slideset).

    3. Disease Information:
      1. Breakbone Fever (i.e., Dengue Fever (DF), Dengue Hemorrhagic Fever (DHF), Dengue Shock Syndrome (DSS)) :
        1. Pathogenesis Mechanism: Both syndromes, DF and DHF/DSS, are caused by any of the four dengue serotypes that belong to the family Flaviviridae (Guzman and Kouri, 2004). The pathogenesis of DHF/DSS is not very well understood nor are the host conditions that favor the severe disease; however, children, females, individuals with chronic diseases such as asthma and diabetes, and whites appear to be at greater risk. Finally, recent reports argue the risk of DHF/DSS is higher if the interval is longer between primary and secondary dengue infection (Guzman and Kouri, 2004). Although most dengue infections cause only mild clinical disease, understanding the basis of severe dengue disease is an important clinical and scientific goal. Dengue viruses are capable of replicating in many cell types and can be detrimental to cell function. However, the major target for dengue virus infection in vivo appears to be cells of the monocyte/macrophage lineage, in which dengue virus causes little cytopathic effect. It is thought that capillary leakage in DHF results from the release of circulating factors by dengue virus-infected monocytes, activated T cells and other cells. Hemorrhagic manifestations, on the other hand, may be multifactorial due to the direct and indirect effects of dengue virus infection on platelets and the coagulation system. Explanations for the occurrence of severe dengue disease have focused on possible viral and host factors. The available evidence supports the suggestion that severe dengue disease can be more frequently observed with some viral strains than others and that it can occur in the absence of 'enabling' host factors. However, the molecular basis for such an association, if any exists, remains unknown. There is also substantial evidence that the risk of DHF is increased during secondary dengue infections and this immunologic mechanism may predominate in the pathogenesis of capillary leakage. In vitro studies have identified both antibody and T-cell-dependent mechanisms that could exacerbate disease, and clinical studies have correlated the presence of enhancing antibodies and higher levels of T-cell activation with DHF. Thus, both viral and host factors are probably relevant to determining the risk of severe dengue disease, but the interactions and relative importance of all these factors in influencing the expression of clinical disease have not been established (Rothman, 1997).


        2. Incubation Period: The incubation period for dengue is four to six days (Guzman and Kouri, 2004).


        3. Prognosis: The prognosis in DHF/DSS depends on prevention or early recognition and treatment of shock. In hospitals with long experience of DSS the case fatality rate in DHF can be as low as 0.2%. Once shock has set in the fatality rate may be high (12% to 44%) (Rigau-Perez et al., 1998). Dengue infection can cause a spectrum of illness ranging from mild, undifferentiated fever to illness up to 7 days' duration with high fever, severe headache, retro-orbital pain, arthralgia and rash, but rarely causing death. Dengue Haemorrhagic Fever (DHF), a deadly complication, includes haemorrhagic tendencies, thrombocytopenia and plasma leakage. Dengue Shock Syndrome (DSS) includes all the above criteria plus circulatory failure, hypotension for age and low pulse pressure. DHF and DSS are potentially deadly but patients with early diagnosis and appropriate therapy can recover with no sequelae (Guha-Sapir and Schimmer, 2005). The vast majority of infections, especially in children under age 15 years, are asymptomatic or minimally symptomatic. Population-based studies have shown increasing severity in the clinical features of DF with increasing age of the patient and with repeated infections. Infants and young children may have an undifferentiated febrile disease with a maculopapular rash. Older children and adults may have either a mild febrile syndrome or the classical and even incapacitating disease. Skin eruptions are reported in over 50% of laboratory-confirmed dengue cases in Puerto Rico, more commonly in children and adults with primary infections. There may be a flushing of the face, neck, and chest initially in the febrile period; or a centrifugal maculopapular rash arising on the third or fourth day; or a later confluent petechial rash with round pale areas of normal skin; or a combination of these manifestations (Rigau-Perez et al., 1998).


        4. Diagnosis Overview: Dengue diagnosis can be performed through virus isolation, genome and antigen detection and serological studies. Serology is currently the most widely applied in routine diagnosis. Of course, clinical, geographical, and epidemiological data associated with the patient remain critical considerations when evaluating a laboratory result (Guzman and Kouri, 2004). The definitive diagnosis of dengue virus infection can only be made in the laboratory, and it depends on the isolation of these viruses, the detection of viral antigens or RNA in serum or tissues, or the detection of specific antibodies in the patients' serum (De Paula and Fonseca, 2004). Five serological tests have been used for the diagnosis of dengue infection: hemagglutination-inhibition (HI), complement fixation (CF), neutralization test (NT), immunoglobulin M (IgM) capture enzyme linked immunosorbent assay (MAC-ELISA) and indirect immunoglobulin G ELISA. The limitations of these techniques are the high cross-reactivity observed with these tests, requiring a comprehensive pool of antigens, including all four serotypes, another flavivirus (yellow fever virus, Japanese encephalitis virus, or St. Louis encephalitis virus), and in some areas, another virus that causes similar clinical manifestations but that is not flavivirus, such as Oropouche, Mayaro or Chikungunya viruses. Furthermore, the dengue antibodies are better detected around the fifth day of disease onset, making this technique unfeasible for rapid diagnosis (De Paula and Fonseca, 2004)


        5. Symptom Information :
          • Syndrome -- Undifferentiated Fever:
            • Description: Infants and young children usually develop an undifferentiated febrile disease that can be accompanied by a maculopapular rash (Guzman and Kouri, 2004).
          • Syndrome -- Dengue Fever:
            • Description: The clinical features of dengue vary frequently, according to the age of the patient. Infants and young children may have an undifferentiated febrile disease with a maculopapular rash. Older children and adults may have either a mild febrile syndrome or the classical incapacitating disease with abrupt onset and high fever, severe headache, pain behind the eyes, muscle and joint-pains, and rash. Skin hemorrhages (with positive tourniquet test and or/petechiae) may be present. Leukopenia is usually found and thrombocytopenia may be observed. The case fatality rate is exceedingly low (Pan American Health Organization, 1994). Clinical description: An acute febrile illness characterized by frontal headache, retro-ocular pain, muscle and joint pain, and rash (Pan American Health Organization, 1994). Dengue virus infections may be asymptomatic or lead to a range of clinical presentations, even death. The incubation period is 4-7 days (range 3-14). Typically, DF is an acute febrile illness characterised by frontal headache, retroocular pain, muscle and joint pain, nausea, vomiting, and rash. The febrile, painful period of DF lasts 5-7 days, and may leave the patient feeling tired for several more days. A biphasic or "saddleback" fever curve is not the norm. Dengue virus disappears from the blood after an average of 5 days, closely correlated with the disappearance of fever, and no carrier state ensues (Rigau-Perez et al., 1998).
            • Observed: Dengue is the most prevalent mosquito-borne viral infection worldwide, with 100 million cases of dengue fever (DF) and half a million cases of dengue haemorrhagic fever (DHF) annually (Malavige et al., 2006). Today, DF and DHF/DSS are considered the most important arthropod-borne viral diseases in terms of morbidity and mortality. More than 2.5 billion people are at risk of infection and more than 100 countries have endemic dengue transmission. DHF has been reported in 60 of them. The burden of DF and DHF disease is not very well documented; however in 1998 alone, more than 1.2 million cases were reported to the World Health Organization, with south-east Asia, the western Pacific and more recently the Americas being the most affected regions (Guzman and Kouri, 2004).


              • Symptoms Shown in the Syndrome:

            • Abdominal pain:
              • Ontology: UMLS:C0000737
            • Bleeding manifestations:
            • Diarrhoea:
              • Ontology: UMLS:C0011991
            • Fever:
              • Ontology: UMLS:C0015967
              • Description: The most severe cases of dengue fever are usually seen in older children and are characterised by a rapidly rising temperature (greater than or equal to 39 C) that lasts 5-6 days (Mairuhu et al., 2004).
              • Observed: 76-100% in Thai adults with classical dengue fever (Pan American Health Organization, 1994).
            • Flushed appearance:
            • Gum bleeding:
              • Ontology: UMLS:C0017565
              • Description: Minor haemorrhagic manifestations like petechiae, epistaxis, and gingival bleeding do occur (Mairuhu et al., 2004).
              • Observed: 3% in patients with dengue fever had gum bleeding (Malavige et al., 2006).
            • Headache:
              • Ontology: UMLS:C0018681
              • Description: The febrile period is accompanied by severe headache, reto-orbital pain, myalgia, arthralgia, nausea, and vomiting (Mairuhu et al., 2004).
              • Observed: 78.8% in patients with dengue fever had headaches (Malavige et al., 2006).
            • Hepatomegaly:
              • Ontology: UMLS:C0019209
            • Leukopenia:
              • Ontology: UMLS:C0023530
            • Lymphadenopathy:
              • Ontology: UMLS:C0497156
            • Maculopapular rash:
              • Ontology: UMLS:C0423791
              • Description: Over half of infected people report a rash during the febrile period that is initially macular or maculopapular and becomes diffusely erythematous, sparing small areas of normal skin ("islands of white in a sea of red") (Mairuhu et al., 2004).
              • Observed: 26-50% in Thai adults with classical dengue fever (Pan American Health Organization, 1994).
            • Myalgia/Arthralgia:
              • Ontology: UMLS:C0231528 C0003862
            • Petechiae or ecchymosis:
              • Ontology: UMLS:C0031256 C0013491
            • Positive Tourniquet Test:
              • Ontology: UMLS:C0242133
              • Description: A positive tourniquet test (more than 20 petechiae in a square patch of skin 2.5 x 2.5 cm [greater than 20/in(2)]) may be found in over one-third of patients with DF (Rigau-Perez et al., 1998). The tourniquet test is another stumbling block, because there is confusion in the definition of a positive result (either ten or 20 petechiae per square inch [6.45 cm2]), it is a long test (5 min) for a doctor's visit, and it feels even longer for the patients, since it is very uncomfortable.The omission of the use of the tourniquet test has considerable impact on the detection of dengue haemorrhagic fever. Grade I dengue haemorrhagic fever, which might represent 15-20% of all dengue haemorrhagic fever cases, depends on tourniquet test positivity (Rigau-Perez, 2006).


                • Positive Tourniquet Test (CDC Dengue Slideset):



                  Description: This slide demonstrates what a typical positive result from a tourniquet test may look like. This patient has more than 20 petechiae per square inch. Source: CDC (CDC Dengue Slideset)
              • Observed: 26-50% in Thai adults with classical dengue fever (Pan American Health Organization, 1994).
            • Thrombocytopenia:
              • Ontology: UMLS:C0040034
            • Vomiting:
              • Ontology: UMLS:C0042963
              • Description: The febrile period is accompanied by severe headache, reto-orbital pain, myalgia, arthralgia, nausea, and vomiting (Mairuhu et al., 2004).
              • Observed: 54.5% in patients with dengue fever had vomiting (Malavige et al., 2006).
          • Syndrome -- Dengue Hemorrhagic Fever:
            • Description: Today, secondary infection by a different dengue serotype is considered the most significant individual risk factor for DHF/DSS. The presence of circulating non-neutralizing, cross-reactive antibodies in a previously immune individual allows for enhancement of infection, favoring the increased entrance of the virus into the target cell through the cell Fc receptor (Guzman and Kouri, 2004). Clinical Case Definition for Dengue Hemorrhagic Fever. The following must all be present: 1. Fever or recent history of acute fever. 2. Hemorrhagic tendencies, as evidenced by at least one of the following: positive tourniquet test, petechiae, ecchymoses, or purpura; and bleeding from mucosa, gastrointestinal tract, injection sites, or others. 3. Thrombocytopenis [100,000 mm(3) or less]. 4. Plasma leakage due to increased capillary permeability as mainifested by at least one of the following: hematocrit on presentation that is greater than or equal to 20% above average for that age, sex, and population; greater than or equal to 20% drop in hematocrit following treatment; or commonly associated signs of plasma leakage-pleural effusion, ascites, and hypoproteinemia (Pan American Health Organization, 1994). DHF commonly begins with a sudden rise in temperature and other symptoms resembling DF. The temperature is typically high (38-40 C) and continues for 2-7 days. DHF and dengue shock usually develop around the third to seventh day of illness. The most common haemorrhagic feature is a positive tourniquet test (over 50% of patients). Petechiae, easily bruised skin, and subcutaneous bleeding at venepuncture sites are present in most cases. Transudate due to excessive capillary permeability collects at the pleural and abdominal cavities (Rigau-Perez et al., 1998).
            • Observed: Dengue is the most prevalent mosquito-borne viral infection worldwide, with 100 million cases of dengue fever (DF) and half a million cases of dengue haemorrhagic fever (DHF) annually (Malavige et al., 2006). Today an estimated 50-100 million cases of dengue fever and 500,000 cases of DHF, resulting in around 24,000 deaths, occur annually, depending on the epidemic activity (Mairuhu et al., 2004).


              • Symptoms Shown in the Syndrome:

            • Abdominal pain:
              • Ontology: UMLS:C0000737
              • Description: Several symptoms and signs occur before defervescence and may serve as warning signs that DHF and DSS are impending: generalised abdominal pain, persistent vomiting, change in the level of consciousness, a sudden drop in the platelet count, and a rapid rise in the hematocrit (Mairuhu et al., 2004).
              • Observed: 14% in patients with dengue hemorrhagic fever had abdominal pain (Malavige et al., 2006).
            • Bleeding manifestations:
              • Description: Haemorrhagic manifestation usually appear after 3-4 days and may vary from a positive tourniquet test and petechiae to haemorrhage from the gastrointestinal tract, nose, and gums (Mairuhu et al., 2004).
              • Observed: 49.3% in patients with dengue hemorrhagic fever had bleeding manifestations (Malavige et al., 2006).
            • Confluent petechial rash:
              • Description: Haemorrhagic manifestation usually appear after 3-4 days and may vary from a positive tourniquet test and petechiae to haemorrhage from the gastrointestinal tract, nose, and gums (Mairuhu et al., 2004).
              • Observed: 1-25% in Thai children with classical dengue hemorrhagic fever (Pan American Health Organization, 1994).
            • Diarrhoea:
              • Ontology: UMLS:C0011991
            • Fever:
              • Ontology: UMLS:C0015967
            • Flushed appearance:
              • Observed: 44% in patients with dengue hemorrhagic fever had a flushed appearance (Malavige et al., 2006).
            • Gastrointestinal bleeding:
              • Ontology: UMLS:C0017181
              • Description: Haemorrhagic manifestation usually appear after 3-4 days and may vary from a positive tourniquet test and petechiae to haemorrhage from the gastrointestinal tract, nose, and gums (Mairuhu et al., 2004).
              • Observed: 1-25% in Thai children with classical dengue hemorrhagic fever (Pan American Health Organization, 1994).
            • Gum bleeding:
              • Ontology: UMLS:C0017565
              • Description: Haemorrhagic manifestation usually appear after 3-4 days and may vary from a positive tourniquet test and petechiae to haemorrhage from the gastrointestinal tract, nose, and gums (Mairuhu et al., 2004).
              • Observed: 6% in patients with dengue hemorrhagic fever had gum bleeding (Malavige et al., 2006).
            • Headache:
              • Ontology: UMLS:C0018681
              • Description: The febrile period is accompanied by severe headache, reto-orbital pain, myalgia, arthralgia, nausea, and vomiting (Mairuhu et al., 2004).
              • Observed: 60% in patients with dengue hemorrhagic fever had headaches (Malavige et al., 2006).
            • Haematemesis:
              • Ontology: UMLS:C0018926
              • Observed: 6% in patients with dengue hemorrhagic fever had haematemesis (Malavige et al., 2006). 38% of Puerto Ricans cases confirmed with with dengue hemorrhagic fever in the laboratory (Malavige et al., 2006).
            • Hepatomegaly:
              • Ontology: UMLS:C0019209
            • Hypotension:
              • Ontology: UMLS:C0020649
            • Leukopenia:
              • Ontology: UMLS:C0023530
            • Lymphadenopathy:
              • Ontology: UMLS:C0497156
            • Melena:
              • Ontology: UMLS:C0025222
              • Observed: 10.3% in patients with dengue hemorrhagic fever had melena (Malavige et al., 2006). 17% of Puerto Ricans cases confirmed with with dengue hemorrhagic fever in the laboratory (Malavige et al., 2006).
            • Myalgia/Arthralgia:
              • Ontology: UMLS:C0231528 C0003862
            • Petechiae or ecchymosis:
              • Ontology: UMLS:C0031256 C0013491
            • Pleural effusions or ascites:
              • Ontology: UMLS:C0003962
              • Description: A prospective study recorded pleural effusions in 84% (22/26) of DHF cases and the mean pleural effusion index (the proportion of the width of the right hemithorax occupied by a pleural effusion in the right lateral decubitus chest radiograph) was 14.1% (Rigau-Perez et al., 1998).


                • Pleural Effusion Index (CDC Dengue Slideset):



                  Description: Here we see a right lateral decubitus X-ray showing a large pleural effusion, typical of DHF the day after defervescence. When the chest X-ray is taken in this position, with the patient resting on the right side, the degree of plasma leakage may be quantified by means of the pleural effusion index. The pleural effusion index is calculated as 100 times the maximum width of the right pleural effusion, divided by the maximal width of the right hemithorax. Source: Vaughn DW, Green S, Kalayanarooj S, et al. Dengue in the early febrile phase: viremia and antibody responses. J Infect Dis 1997; 176:322-30 (CDC Dengue Slideset).
              • Observed: 14.7% in patients with dengue hemorrhagic fever had pleural effusions or ascites (Malavige et al., 2006).
            • Positive Tourniquet Test:
              • Ontology: UMLS:C0242133
              • Description: A positive tourniquet test (more than 20 petechiae in a square patch of skin 2.5 x 2.5 cm [greater than 20/in(2)]) may be found in over one-third of patients with DF (Rigau-Perez et al., 1998).


                • Positive Tourniquet Test (CDC Dengue Slideset):



                  Description: This slide demonstrates what a typical positive result from a tourniquet test may look like. This patient has more than 20 petechiae per square inch. Source: CDC (CDC Dengue Slideset)
              • Observed: 76-100% in Thai children with classical dengue hemorrhagic fever (Pan American Health Organization, 1994).
            • Splenomegaly:
              • Ontology: UMLS:C0038002
            • Thrombocytopenia:
              • Ontology: UMLS:C0040034
            • Vaginal bleeding:
              • Ontology: UMLS:C0151706
            • Vomiting:
              • Ontology: UMLS:C0042963
              • Description: Several symptoms and signs occur before defervescence and may serve as warning signs that DHF and DSS are impending: generalised abdominal pain, persistent vomiting, change in the level of consciousness, a sudden drop in the platelet count, and a rapid rise in the hematocrit (Mairuhu et al., 2004).
              • Observed: 68% in patients with dengue hemorrhagic fever had vomiting (Malavige et al., 2006). 62% of Puerto Ricans cases confirmed with with dengue hemorrhagic fever in the laboratory had vomiting (Malavige et al., 2006).
          • Syndrome -- Dengue Shock Syndrome:
            • Description: The World Health Organisation defines DSS as DHF with circulatory failure as manifested by a rapid, weak pulse with narrowing of the pulse pressure (less than or equal to 20 mmHg, regardless of pressure levels, e.g. 100/90 mmHg) or hypotension with cold, clammy skin and restlessness. In Asia, DHF and DSS mainly affect children under 15 years of age in hyperendemic areas. The age distribution is different in the Americas, where these syndromes occur in all age groups. However, the majority of fatalities during epidemics in the Americas occur in children (Mairuhu et al., 2004). In severe cases, the patient's condition suddenly deteriorates after a few days of fever. At the time of or shortly after the temperature drop, between 3 and 7 days after onset, there are signs of circulatory failure: the skin becomes cool, blotchy, and congested; circumoral cyanosis is frequently observed, and the pulse becomes weak and rapid. Although some patients may appear lethargic, they become restless and then rapidly go into a critical stage of shock. Acute abdominal pain is a frequent complaint shortly before the onset of shock (Pan American Health Organization, 1994). The liver may be palpable and tender; and liver enzymes are usually mildly abnormal but jaundice is rare. The four warning signs for impending shock are intense, sustained abdominal pain; persistent vomiting; restlessness or lethargy; and a sudden change from fever to hypothermia with sweating and prostration. The development of any of these signs or any suggestion of hypotension are indications for hospital admission and management to prevent shock. The patient may recover rapidly after volume replacement but shock may recur during the period of excessive capillary permeability. The prognosis in DHF/DSS depends on prevention or early recognition and treatment of shock. In hospitals with long experience of DSS the case fatality rate in DHF can be as low as 0.2%. Once shock has set in the fatality rate may be high (12% to 44%) (Rigau-Perez et al., 1998).
            • Observed: 26-50% in Thai children with classical dengue hemorrhagic fever developed shock (Pan American Health Organization, 1994). 18.7% in patients with dengue hemorrhagic fever developed shock (Malavige et al., 2006).
          • Syndrome -- Dengue Fever-Unusual Manifestations:
            • Description: An increasing number of dengue infections have been related to other unusual manifestations. These include dengue fever with severe haemorrhage, fulminant liver failure, cardiomyopathy, and neurological phenomena such as altered consciousness, convulsions, and coma resulting from enchephalitis and encephalopathy. Previously, neurological manifestations were ascribed to nonspecific complications secondary to DHF and DSS. Possible causes of dengue encephalopathy include hypotension, cerebral oedema, focal haemorrhage, hyponatraemia, and fulminant hepatic failure. However, a recently documented possibility is the invasion of the central nervous system. Other unusual presentations include ocular manifestations (Mairuhu et al., 2004).

        6. Treatment Information:
          • Suppportive Treatment: Treatment is supportive and includes bed rest, anitpyretics, and analgesics. In case of dehydration, fluid and electrolyte replacement are used in addition (Burke and Monath, 2001). Ribavirin has marginal value (Burke and Monath, 2001).

    4. Prevention:
      1. Environmental Management-Naturalistic Methods:
        • Description: Naturalistic methods involve changes to the natural environment designed to suppress the abundance of immature stages of vector mosquitoes. These measures may be either long-term, which are based on filling or draining of potential aquatic breeding sites for the vector, or short-term. On occasion, A. aegypti may breed in newly-constructed or abandoned septic tanks or latrines, and this may be prevented by draining or filling. More temporary naturalistic measures may include landscaping efforts to remove the vegetation that provides shade, food, or water collection that might contribute to the abundance of these vector mosquitoes; vegetation near the home may influence the abundance of A. aegypti. Where possible, brush should be cut back or removed from the immediate vicinity of homes. Treeholes and other natural rainwater receptacles should be filled with concrete, sand, packed earth, gravel, or other suitable materials. Stumps and other vegetation near houses that could become foci should be removed, or at least cut back annually (Pan American Health Organization, 1994).
      2. Improved Domestic Water Supply:
        • Description: One of the keys to the control of urban Aedes vectors, particularly A. aegypti, is improved domestic water supply (Pan American Health Organization, 1994). Potable water must be delivered in sufficient quantity, quality, and consistency year-round in order to reduce the use of major breeding sites, duchas, drums, overhead tanks, and jars. Individual household piped water supplies are the preferred alternative to the use of wells, communal standpipes, rooftop catchments, and other water delivery systems (Pan American Health Organization, 1994).
        • Efficacy:
          • Rate: We investigated the hypothesis that a deficient supply of